It is well known in ordinary photographic process and diffusion transfer photographic process that a temporary barrier layer may be provided between layers in a photographic element into which a processing solution penetrates. Particularly in the diffusion transfer process, where a neutralizing system is used for the purpose of stopping development, stabilizing the image, or like purpose, it is well known that such a temporary barrier layer may be used in the neutralizing system for the purpose of "timing" the neutralization to prevent the neutralizing layer from neutralizing the developing solution faster than required and hence keep the maximum density constant. A temporary barrier layer to be used for such a purpose is called a timing layer. Examples of such a timing layer are disclosed in U.S. Pat. Nos. 4,061,496, 4,056,394, and 4,201,587, and Japanese Patent Application (OPI) Nos. 72622/78 (corresponding to U.S. Pat. No. 4,199,362), and 141644/82 (the term "OPI" as used herein means an "unexamined published aplication").
In general, the development reaction in silver halide photographic process proceeds slowly at a low temperature but proceeds more rapidly at an elevated temperature. Accordingly, if the diffusion transfer process is used in instant photography where, unlike in the ordinary photographic process wherein the temperature for development may be controlled, the photographic material must be capable of consistent development despite various temperatures. It is therefore extremely important to make the neutralization system of the photographic element capable of compensating for the fluctuation in rate of development due to fluctuation in temperature, i.e., to accelerate the neutralization of the developing solution at an elevated temperature where the development reaction proceeds more rapidly but retard the neutralization of the developing solution at a low temperature where the development reaction proceeds slowly. In this manner, it is possible to obtain an excellent image regardless of development temperature. A large number of examples of timing layers having such a temperature compensation function are disclosed in the foregoing patents.
In the so-called monosheet type diffusion transfer photography, a phenomenon called "aftertransfer" is often observed over the maximum density portion, gradation portion, and minimum density portion with the passage of time (a few days to a few weeks) after formation of image. This phenomenon remarkably deteriorates the picture quality. In this phenomenon, while most of the dye released upon processing migrates to the mordant layer, some of the dye released is left in layers other than the mordant layer. The dye thus left in other layers gradually migrates to the mordant layer with the passage of time. This causes aftertransfer. The cover sheet containing such a timing layer as disclosed in the foregoing patents is not effective in inhibiting such a phenomenon. Even if the timing layer has somewhat of an effect, it is disadvantageous in that the transfer image has a poor sharpness.
Japanese Patent Application (OPI) No. 19137/85 made it possible to inhibit afertransfer without deteriorating sharpness by using a photographic element. Specifically, in a neutralizing system for lowering the pH of an alkaline processing solution, the processing solution neutralizing process proceeds by two different stages. (The neutralizing system consists of a neutralizing layer and a timing layer which is directly or indirectly laminated above or under the neutralizing layer in a positional relationship such that the alkaline processing solution reaches the neutralizing layer through the timing layer.) More specifically, the photographic element as disclosed in Japanese Patent Application (OPI) No. 19137/85 is characterized in that the neutralization reaction proceeds by at least two stages such that in the first stage the pH of the processing solution (photographic system) is lowered to the extent that the development and dye release reaction is interrupted while the transfer of a dye for forming a transfer image can continue, and in the second stage the pH of the processing solution (photographic system) is gradually lowered to a final value withstanding prolonged storage, as a result of which the dye remains immobilized and the image remains stable. The first neutralizing stage is preferably characterized by a rapid pH change. This is a so-called "inverted S-shaped" pH drop in which the pH value shows a rapid drop after being maintained high for a certain period of time. On the contrary, the second neutralizing stage is preferably characterized by a relatively slow pH drop. However, the second neutralizing process may show an inverted S-shaped pH drop. Such a two-stage neutralizing process can be accomplished with a neutralizing system layer prepared by coating on a support a neutralizing layer, a second timing layer, an auxiliary neutralizing layer, and a first timing layer in this order. Alternatively, if a neutralizing layer capable of gradual neutralization is used, a second timing layer can be omitted. In this case, the neutralizing system layer can be provided by coating on a support such a neutralizing layer, an auxiliary neutralizing layer, and a first timing layer in this order.
The pH drop process (mode) can be freely controlled by properly adjusting the component, composition and added amount of the above described timing layer. That is, the period (x) during which the pH is maintained high can be adjusted by the first timing layer, the pH drop at the first stage can be controlled by the auxiliary neutralizing layer, and the pH drop process after the period x can be controlled by the second timing layer and the neutralizing layer. The afertransfer can be effectively inhibited by properly adjusting the neutralizing process. The more positive temperature coefficient the first timing layer has, i.e. the lower the temperature of the first timing layer is, the longer is timing. In other words, the first timing layer preferably is slow in neutralization.
On the other hand, U.S. Pat. No. 4,356,249 describes an improvement in the processing temperature dependence of a color diffusion transfer photographic film unit (assemblage) containing a positive redox compound as a dye image forming compound. In accordance with the above described U.S. patent, the improvement can be accomplished by providing first and second timing layers and an auxiliary neutralizing layer as an additional neutralizing layer between the first timing layer and the second timing layer. (The first timing layer has a negative temperature coefficient.) In this photographic system, the above described auxiliary neutralizing layer is designed to inhibit the release of a dye from the positive redox compound involved in the development of silver halide to a much higher extent at a low temperature than at an elevated temperature in order to improve the processing temperature dependence of the system. Thus, this photographic system is not intended to inhibit the afertransfer of a diffusive dye released from the positive redox compound. Accordingly, this photographic system has no effect of inhibiting afertransfer.
An image formed by processing may be gradually deteriorated even in a dark place particularly when stored at an elevated temperature and a high humidity. This causes a remarkable deterioration of picture quality. Particularly, magenta dyes are subject to discoloration due to their structure. In effect, however, such a discoloration is often offset by the above described aftertransfer which causes a color intensification. However, if a neutralizing system as disclosed in Japanese Patent Application (OPI) No. 19137/85 is used to inhibit aftertransfer, discoloration is more remarkable than color intensification. Accordingly, the photographic system containing such a neutralizing system is disadvantageous in that it is subject to deterioration of picture quality after being stored at an elevated temperature and a high humidity.
Thus, it has been desired to improve the picture quality preservability so that a complete system free of color intensification or discoloration can be obtained.